The invention relates to a process for connecting functional elements to a shaft, to a shaft produced by the process according to the invention and to the use of said shaft in a comminutor.
Apparatuses such as, for example, mixers, kneaders, stirrers or comminutors comprise shafts on which various functional elements are received. Examples of functional elements are bars, blades, arms, hooks, journals, helices, paddles, knives or studs. By the selection of the functional element, the shaft can be adapted to the required tasks.
On account of the size and complexity of the parts, the functional elements and the shaft are not generally produced from one piece. It is therefore necessary to connect the functional elements to the shaft using a suitable joining process. The joining processes include, by way of example, pressing-in, soldering and welding.
In the case of pressing-in, the two parts being joined are elastically deformed in the presence of force and pressed into one another. Undesirable release is prevented by a force fit, and the two parts being joined can be separated from one another again by applying sufficient force.
In the case of soldering, the two parts being joined are connected to one another by melting a solder. The melting temperature of the solder here is considerably lower than the melting temperature of the parts to be joined.
In the case of welding, the two parts being joined are heated to above the melting temperature thereof, such that they are firmly connected to one another following resolidification. Additional material may optionally be introduced in this case by way of a weld filler. By the fusion of the two parts being joined, it is possible to produce a very firm integral bond. The welding can be carried out with the aid of various techniques, for example by means of fusion gas welding, arc welding or metal inert gas welding.
Since it is possible to achieve very firm integral bonds between a functional element and a shaft by welding, the welding processes are preferred to other joining techniques. In order to make a welded joint between a functional element and a shaft, grooves for receiving the functional elements are cut into the shaft. Then, the functional elements are placed into the grooves and connected to the shaft by way of an all-round welded seam. This process has the disadvantage that the faces of the components placed in the groove cannot be reached, and therefore the faces placed in the groove cannot be connected to the shaft by a welding process. In addition, each welding operation gives rise to what is known as a metallurgical notch. In the event of loading, microcracks, which can later lead to fracture, can form starting from the metallurgical notch. It is problematic in this respect that this metallurgical notch coincides with a shaped notch, which here is formed by the groove. As a result of the groove, the material is weakened at this site and represents a potential site of fracture. Tearing of the welded joint between a functional element and the shaft must be prevented, however, since this leads to the failure of the component and therefore to a stoppage in production.
It is an object of the invention to provide a process for connecting functional elements to a shaft which reduces the risk of fracture of the welded joint between the functional element and the shaft. In this case, the intention in particular is to avoid the co-occurrence of a shaped notch and a metallurgical notch. It is a further object of the invention to provide a robust shaft with bars received on the shaft for use in a comminutor.